Currently, several pen systems are available for subcutaneous substance delivery. These pen systems typically use 31 gauge needles having a length of about 8 mm and are used to deliver the contents of a cartridge, such as insulin, to patients rapidly and as painlessly as possible. Additional details of intradermal drug delivery have been previously described in U.S. patent application Ser. No. 09/835,243, filed Apr. 13, 1999, and Ser. No. 09/417,671 filed Oct. 14, 1999, the entire content of each application being incorporated herein by reference.
Although currently available pen systems utilize designs manufactured to maximize patient comfort, a need exists for a “microneedle” pen system which can offer an inherent advantage in the reduced pain and sensation to the user resulting from the minimal penetration associated with the extremely small microneedles used. Such microneedle drug delivery systems however, require shorter needles, typically less than or equal to 3 mm, and smaller diameters of 34 gauge or less. Such needle lengths and gauges are required due to depth constraints and bevel edge openings, which are required to access only the deep intradermal or shallow subcutaneous tissue space. Simple modification of current pen systems used for subcutaneous delivery is not possible because of severe engineering constraints associated with the size and volume restrictions imposed by the use of microneedles.
Therefore, a need exists to provide a system and method for the incorporation of microneedle systems as the pen outlet, or user interface. As this results in significant changes in the in vitro and in vivo function of the pen system, additional engineering requirements and methods of use are also required for the effective function of the pen device.